docs: def get_ss_class(pdb_file, dssp_file, chain):
      """Define the secondary structure class of a PDB file at the specific chain
  
      Args:
          pdb_file:
          dssp_file:
          chain:
  
      Returns:
  
      """
      prag = pr.parsePDB(pdb_file)
      pr.parseDSSP(dssp_file, prag)
      alpha, threeTen, beta = get_dssp_ss_content_multiplechains(prag, chain)
  
      if alpha == 0 and beta > 0:
          classification = 'all-beta'
      elif beta == 0 and alpha > 0:
          classification = 'all-alpha'
      elif beta == 0 and alpha == 0:
          classification = 'mixed'
      elif float(alpha) / beta >= 20:
          classification = 'all-alpha'
      else:
          classification = 'mixed'
  
      return classification